Despite major advances in both surgical and non-surgical revascularization, therapeutic options for many patients with lower extremity vascular disease remain limited. In particular, the prognosis for patients with chronic critical leg ischemia is often poor, and is compounded by the lack of efficacious drug therapy. Angiogenic growth factors, the therapeutic implications of which were identified by the pioneering work of Folkman and colleagues over two decades ago constitute a potentially novel form of therapy for such patients. The feasibility of using recombinant formulations of angiogenic growth factors to expedite and/or augment collateral artery development in animal models of myocardial and hindlimb ischemia - "therapeutic angiogenesis" - has been established and confirmed by several laboratories, including our own. These preliminary studies have suggested that two angiogenic growth factors in particular, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), are sufficiently potent to merit further investigation. More recently, experiments performed in our laboratory have indicated that in the case of VEGF - unlike bFGF, a secreted protein - similar results may be achieved by percutaneous arterial gene transfer. The ultimate utility of either recombinant protein administration or arterial gene therapy for critical leg ischemia, however, requires that a number of outstanding issues be further elucidated. Accordingly, the experiments outlined in this Proposal have been designed to accomplish three specific aims. First, we will define certain morphologic, temporal, and functional aspects of therapeutic angiogenesis: these experiments will document the time-course of cellular proliferation, examine the impact of pre-established collaterals, and investigate preservation of endothelium- dependent flow in response to these therapeutic strategies. Second, we will investigate certain conditional factors which may modulate the outcome of therapeutic angiogenesis: these experiments will determine the impact of hypoxia, hypercholesterolemia and experimentally induced diabetes on the cellular and/or host response to therapeutic angiogenesis. Third, we will define the impact of growth factor selection, mode of delivery and use of adjunctive therapies in optimizing the anatomic and physiologic outcomes of therapeutic angiogenesis: the facilitatory effects of combination bFGF/VEGF, adjunctive therapy with heparin, and coincident activation of plasminogen; the impact of intravenous and intramuscular as opposed to intra-arterial delivery; and the impact of gene therapy using alternative VEGF isoforms will be studied. These studies will be performed in vitro and in vivo; the latter will employ a rabbit model of unilateral hindlimb ischemia. Preliminary work in our laboratory suggests that these studies may yield promising insights into the fundamental basis for native as well as therapeutic angiogenesis, and at the same time more explicitly define the manner in which therapeutic angiogenesis may be successfully incorporated into clinical practice.